Solved!

[Nix]

On 5 Feb 2009, Michel Dänzer told this:
> On Thu, 2009-02-05 at 00:29 +0000, Nix wrote:
>> (The performance reduction for non-antialiased client-side fonts is
>> probably down to xterm: with konsole, they're equally fast.)
>
> Yeah, it could be that xterm hits one of the cases the glyph cache
> doesn't handle well yet. Or maybe it renders each glyph separately
> instead of at least a whole line (or as much of it as possible anyway)
> at once?

It seems to be spending vast amounts of time inside wcwidth(), so I
suspect at least one O(n^2) work-over-the-line somewhere...

>> So it looks like I'm going to be using prerelease X servers, and I owe
>> Owen Taylor a beer for implementing the glyph cache and Michel Dänzer
>> another beer for making it work with non-antialiased fonts :)
>
>:)

I jinxed it by sending that email :(((

-- 
`We must stand together and fight for our shared cultural heritage as a
 group of people who cannot stand together to fight for our shared
 cultural heritage.' --- jspaleta on Balkan balkanization